Patent GB-644914-A (GB)
Title: Process of chlorinating acetaldehyde
IPC: C07C45/63
Filed: 1947-05-31
Abstract: Acetaldehyde, which may be in the form of paraldehyde, is chlorinated in two or more stages, in the first stage acetaldehyde, water, and chlorine are continuously fed into a reaction vessel with cooling, the amount of chlorine fed being in excess of one mol. per mol. of acetaldehyde fed and the molar ratio of water to aldehyde being 3.5 or greater, the reaction vessel is allowed to fill up and overflow and the reaction mixture is continuously collected and in the second stage chlorine is continuously dispersed into the collected reaction mixture while cooling to maintain the temperature higher than that in the first chlorination.  A solution containing dichloracetaldehyde in high yield is obtained and this may be further chlorinated to produce a solution of chloral by extending the chlorination to a four-stage continuous system.  Thus the reaction mixture overflowing from the second stage is continuously dispersed with chlorine while allowing the temperature to rise above that of the second chlorination stage and the reaction mixture from the third stage is then collected and continuously dispersed with chlorine while allowing the temperature to rise above that in the third stage, thus effecting still further chlorination of the acetaldehyde. Alternatively, the reaction mixture overflowing from the second stage may be chlorinated in batches, the temperature of the batch being raised gradually and the chlorination being completed when the temperature of each batch is raised to the same final temperature attained in the fourth stage of the continuous process.  The four-stage process and the batch chlorination process should be effected until the dichloracetaldehyde content of the mixture overflowing from the fourth stage or from each batch chlorination is maintained below 3 per cent by weight.  The temperature in the first stage is preferably 5 DEG  to 15 DEG  C. and the molar ratio of water to acetaldehyde is preferably within the range 3.5 to 4.5 and the molar ratio of absorbed chlorine to acetaldehyde fed in the first stage is preferably within the range 1.5 to 2.0.  In the second stage the temperature should be from 25 DEG  to 35 DEG  C. and the amount of chlorine absorbed in this stage should be such as to bring the total amount of chlorine absorbed in both chlorinations to between 1.9 and substantially 2.1 mols. per mol. of acetaldehyde fed.  The amount of chlorine absorbed in the second stage should be at least 0.1 mol. per mol. of acetaldehyde fed.  By limiting the amount of chlorine absorbed in the first stage to between 1.5 and 1.9 mols. per mol. of acetaldehyde fed and the total amount of chlorine absorbed in the first two stages to substantially 2.0 moles. per mol. of acetaldehyde a high yield of dichloracetaldehyde is obtained in the two-stage process.  To provide chloral, the third stage chlorination temperature should preferably be from 65 DEG  to 75 DEG  C. and the fourth stage chlorination should be 80 DEG  to 90 DEG  C.  In an example, water and paraldehyde are fed with chlorine into a reaction vessel which is allowed to fill and overflow, the temperature being maintained at 10 DEG  to 12 DEG C. by cooling.  The reaction mixture which overflows is chlorinated in a second vessel at about 30 DEG  C.  In the first stage the water-acetaldehyde ratio is 4.24 : 1 and the chlorine-acetaldehyde ratio is 1.88 : 1 and p  the molar ratio of chlorine fed in the second vessel to aldehyde fed to the first vessel is 0.25 : 1.  The mixture from the second stage is further chlorinated in batches, chlorine being dispersed into each batch as its temperature is raised to about 83 DEG  C. and the chlorination is continued until the concentration of dichloracetaldehyde in each batch is below 1 per cent.  Crude chloral containing a small amount of butyl chloral, acetic acid, chlorinated acetic acid and dichloracetaldehyde is obtained. French Specifications 612,396 and 711,095 are referred to.